Brain natriuretic peptide (BNP) is a recently discovered neuropeptide, isolated from the porcine brain, that is highly homologous to atriopeptin (AP), the atrial natriuretic peptide. We used a set of highly selective antisera against the two peptides to map their differential distribution immunohistochemically in the rat central nervous system. BNP immunoreactivity has a distinct distribution, involving many central autonomic and endocrine control structures that contain little if any AP immunoreactivity. AP and BNP belong to a family of neuropeptides that may be important in central cardiovascular control.